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The Cisco® ASR 1000 Series DSP-SPA is a single-width, half-height, high-power shared port adaptor (SPA) digital signal processor (DSP) module that can be used in multiple Cisco platforms (Figure 1). The SPA-DSP provides voice service such as voice transcoding and transrating and dual-tone multifrequency (DTMF) interworking capability for the platforms that support SPA modules.

Figure 1. Cisco ASR 1000 Series DSP-SPA Card

The DSP-SPA helps position a peering session border controller (SBC) with another carrier’s voice-over-IP (VoIP) network and helps provide access to the SBC in the service provider edge, enabling Session Initiation Protocol (SIP) trunking and aggregation of enterprise and residential customers. These cards can also be used when the Cisco ASR 1000 Series Aggregation Services Routers are deployed in Cisco Unified Border Element (CUBE) Enterprise Edition for public-switched telephone network (PSTN) access using SIP trunks. Transcoding is used for voice codec translation between two VoIP networks, as part of the data border element (DBE) functions. Transrating is used for repacketization for packets with the same codec.

Transcoding is the process of translating a media stream encoded using one codec into a media stream encoded using another codec: for example, translating a media stream encoded using G.711 into G.729. It requires DSPs. Customers take two approaches to transcoding (Figure 2). One set of customers expects SBCs to have DSPs on board to perform the transcoding when required (model 1). Another set of customers wants to centralize the DSP resources, so SBCs at the edge offload transcoding to a centralized DSP resource (model 2); this centralized DSP resource could be serving a number of SBCs and providing many other DSP-dependant services in addition to transcoding. The Cisco ASR 1000 Series SBC supports both models.

Figure 2. DSP-SPA in Unified SBC as Transcoder

When deployed in an enterprise customer’s network, the DSP-SPA cards can be used to transcode between a codec required by a SIP service provider and a codec used within the enterprise network. As shown in Figure 2, the DSPs can reside either in the same device (in-box transcoding) or in a different device (out-of-box transcoding).

-The capability to easily add new interfaces as they are needed facilitates a “pay-as-you-grow” business model. SPAs are shared across multiple platforms and can easily be moved from one platform to another, providing consistent feature support, accelerated product delivery, and a significant reduction in operating expenses (OpEx) through common sparing as service needs change.